The implantation of an intraocular lens for restoring vision after cataract surgery is well-known in the art. In general, two forms of surgery are used to remove cataracts. These are extracapsular cataract extraction and intracapsular cataract extraction. (Discussed in U.S. Pat. No. Re. 31,626 to Hoffer).
Both intracapsular and extracapsular extraction eliminate light blockage due to the cataract. In intracapsular extraction the entire lens with the capsule and its content material intact is removed. In extracapsular cataract extraction the clouded cellular material within the lens capsule is extracted through an incision made through the anterior capsule of the lens without removing the transparent rear capsule wall (posterior capsule), suspensory ligaments (zonules) and peripheral portions of the anterior capsule (anterior capsule flaps).
Extracapsular extraction substantially reduces certain post-surgical complications which may result from intracapsular extraction. Particularly, one complication of intracapsular extraction is loss of vitreous humor from the eye through the incision made to accomplish the intracapsular extraction. Another undesirable complication of intracapsular extraction is Cystoid Macula Edema (CME). CME is an edema or swelling of the macula of the retina which may be caused by certain enzymes which are released from the iris and migrate through the vitreous humor back to the macula causing swelling. Vitreous loss and CME are both substantially reduced when extracapsular extraction is used since the posterior capsule remains in place, thereby preventing the vitreous humor from reaching the anterior chamber of the eye.
Following extraction of a cataractus lens, an intraocular lens is normally implanted in either the anterior or posterior chamber of the eye. A major problem associated with use of posterior chamber lenses is impairment of vision by secondary cataractic growth. While the lens capsule is inanimate, it is almost impossible to remove all living cells from it during cataract extraction. As a result, after sometime the cells grow and proliferate forming a bubbly glistening material known as Elschnig's pearls. Eventually the Elschnig's pearls impair vision necessitating subsequent corrective post operative surgery by invasive or non-invasive procedures.
Generally, known non-invasive post-operative corrective surgery such as laser surgery involves destroying the unwanted tissue behind the rear surface of the implanted lens by ionization. Laser surgery must be dimensionally precise to avoid ionizing or otherwise damaging the implanted lens and posterior capsule by radiation. Secondary cataratic growth can alternatively be removed by an invasive surgical procedure known as a discission in which a surgeon inserts a knife behind the lens and makes an opening in the intact posterior capsule. Both laser surgery and the discission procedure are more difficult when the lens implanted is a posterior chamber lens having a rear surface that seats directly against the posterior capsule. When this type of lens is implanted laser surgery can damage the lens. Particularly, the opening in the intact posterior capsule made during laser surgery results from a minor explosion at the point behind the lens where two laser beams intersect. If this explosion is too close to the lens it can cause small flaws or "nicks" in the lens. The lack of space between the rear surface of the lens and the posterior capsule also makes it difficult to perform a discission without displacing the lens.
Several available posterior chamber lenses include a structure which spaces the rear surface of the lens from the posterior capsule to facilitate corrective surgery. One such available posterior chamber lens is described in U.S. Pat. No. Re. 31,626 to Hoffer. The Hoffer lens includes an annular lip at the rear surface of the lens body which spaces the capsule from the edge of the rear surface of the lens. The Hoffer lens has several drawbacks. One disadvantage of the Hoffer lens is that collapse of the posterior capsule directly upon the central portion of the lens rear surface can occur. Another problem with the Hoffer lens is locating the open notch on the posterior of the lens during a discission. This can be difficult for the surgeon since the notch is frequently obscured from view by the iris.
U.S. Pat. No. 4,485,499 to Castleman, describes another type of posterior chamber lens including support structures for separating the lens body from the posterior capsule. One embodiment of the Castleman lens includes a solid annular portion and a central portion which is offset forwardly from the annular portion of the lens. The annular portion provides support for the posterior capsule when implanted but does not include an open space therein for insertion of a discission instrument or free flow of vitreous through the lens. Other supporting structures for the Castleman lens include spaced ridges fastened directly to the rear surface of the lens and spaced pegs connected by filaments. One specific arrangement of supporting pegs and connecting filaments described is a rectangular 4-peg combination with filaments on all four sides of the rectangle or on both sides and diagonals which defines a chamber roof profile for posterior capsule support. None of the embodiments of the Castleman lens include a continuous ring-like posterior resilient seal member which is spaced from and attached to the rear surface of the lens.
U.S. Pat. No. 4,575,877 to Herrick described yet another type of posterior chamber lens with a structure separating the lens body from the posterior capsule. The Herrick lens includes pliable loops each having an arcuate shaped mounting end with a protuberant member. The pliable loops define a posterior capsule framework. As in the case of the Hoffer and Castleman lenses, the Herrick lens does not include a continuous resilient ring-like seal against the posterior capsule.
It is believed that if the surgeon does a good job of cleaning the posterior capsule at the time of cataract extraction, a posterior chamber lens which provides a continuous resilient seal against the posterior capsule below the periphery of the lens when implanted will inhibit growth and migration of Elschnig's pearls into the central area of the posterior capsule, thereby significantly extending the period of time between cataract extraction and post-operative surgery. A continuous ring-like seal spaced from the rear surface of a posterior chamber type will also uniformly support the posterior capsule surface around the entire periphery of the lens to eliminate collapse of the capsule onto the rear surface of the lens. Inclusion of an open zone or free space through the lens at the rear surface of the lens body will facilitate both invasive and non-invasive post operative corrective surgery and provide for improved vitreous movement between the rear surface of the lens and the posterior capsule.
Accordingly, a substantial need exists for an improved posterior chamber lens which when implanted, provides a continuous resilient seal against the posterior capsule and an open zone or free space through the lens between the lens rear surface and the continuous resilient sealing member.